"You have a weird bespoke data structure" is an example of an "environment" where you might not have a sort that works for your data in your standard library. O

"You have a weird bespoke data structure" is an example of an "environment" where you might not have a sort that works for your data in your standard library. Of course, if you're in that situation, you're not using a weird bespoke data structure for a mere few percent better performance.